Exhaust gas turbochargers are provided on an engine to deliver air to the engine intake at a greater density than would be possible in a normal aspirated configuration. This allows more fuel to be combusted, thus boosting the engine's horsepower without significantly increasing engine weight.
Generally, an exhaust gas turbocharger includes a turbine section and a compressor section, and uses the exhaust flow from the engine exhaust manifold to drive a turbine wheel located in the turbine section. The turbine wheel drives a compressor wheel located in the compressor section via a shaft that extends between the sections. Air compressed by the compressor section is then provided to the engine intake as described above.
In some turbochargers, the turbine section may have variable turbine geometry (VTG) that permits adjustment of the amount of exhaust gas directed to the turbine wheel. In some examples, the VTG is implemented using a ring of aerodynamically shaped vanes that are disposed in the turbine housing at the inlet to the turbine wheel. The vanes rotate in unison to vary the inlet area and angle of approach of the exhaust gas directed to the turbine wheel. By altering the turbine housing geometry in this way, the turbocharger has reduced lag and increased efficiency at higher speeds. Moreover, the exhaust gas backpressure and the turbocharger speed can be controlled by modulating the exhaust gas flow to the turbine wheel via the VTG.